I have always thought about the ingenuity that is involved with the construction of a CNC machine and just figured It was out of my ability to build that I would have to buy one and move on…That is until recently when I meet a man who had built one a few years back…Well It did not take me long to realize I have to try and build one so here I am with questions I hope to get answered…So presently I’m in the design state…I have watched a lot of videos from a lot of amazing folks with quite an ability from start to finish and all I can do is take my hat off to them…
Kudos to those of you that understand all the little intricate and details that would go into a build like this…For me I’m lacking in the understanding of a lot of that engineering that would go into a build but am most interested in trying to understand…So please bear with me…I probably will ask a lot of seemingly stupid questions for those of you that are talented

So let me start out by stating I’m trying to build a nice machine that will be used as a hobbyist machine for me and family so something that is built for commercial use will not be factored in however we will try and build as much quality into the design and fab…I was thinking as a bonus It would be nice if it was able to cut aluminum say up to ½” would be a huge plus…I have a budget and am hoping to stay in, I figured around $3K-$3500 range…

I’ll be building this in my garage with basic tools…Drill press, table saw to cut the aluminum, although I was thinking that it may be better to fab all up in wood 1st then come back and cut on a CNC router the aluminum…I also have access to a Mill however I’m a bit weak on its use, but have looked for an excuse to improve…Now with this said my thoughts for the wood was to fine tune my drawings for the various parts with the help of a friend and ask him to possibly cut the aluminum plate on his CNC machine I have stashed…
I have ¼”, ½” and 1” and may consider getting the 2” thick I saw in a pile and purchase that…however this would all be part of the budget…

Anyhow
My intentions is to build a machine with a 4’ x 4’ cutting area…
The platform is going to be 2” x 2” tube steel perhaps .185 thick in the wall so from everything above the “X” linear rail I was thinking would be aluminum…Is the .185 an over kill and I could get away with 11 gauge at .120 thick… savings for better electronics later perhaps

My questions from what sizes of linear rails and trucks including ball screws and how to read the pitch of a ball screw when ordering...I'm thinking the heavier duty the better so I was thinking 25mm trucks and linear rails but if 20mm would do the trick then let's go that route and spend the savings on something else...
Then there's the advertised dimensions on the linear rails and ball screws as to where those are measured from...end to end or block to block...I think I can safely say on the rails from end to end but the ball screws are they a different story...
ex: 1000mm is it from end to end or after both blocks are on, is it from the outside of the blocks or perhaps the inside of the blocks...
Trying to visualize this and hand draw it out for the rendering, so I can get the frame welded together
What size of pitch of ball screws should be considered and would be best suited for what I'm shooting for...I was watching the many videos and there was conversation that some thought was to have the x-y axis the same (I think I remember 10 being mentioned for the X-Y) but then the z would be different (and if I recall it was 5 for the Z) ...

Stepper motors...Open or closed loop...Then there's the size of motor... which size would be best for my performance I'm trying to accomplish...Direct drive would be easier for me to design and build into my work, but, should and if so a gear ratio system like 3-1 be a better choice and if so why? Would have to design this into the design...I’m not speaking of the gear rail on the side just the reduction of a gears on the end of the ball screws and motor…I’m leaning towards 2 motors for the “X” and one motor for the “Y” & “Z”

Then we have the Gantry...for cutting aluminum would a piece of 3 x 6 or 80160 heaviest “T” Extrusion I can find do the job or should I try and figure a way for using steel? And if I use steel what size? More involved and the additional weight vs the "T" slotted extrusion...I had thought about only if needed was to fill the extrusion up with perhaps sand or I might try and find a nice piece of rod and put it in the cavities of the extrusion and fill the rest of the cavity with acrylic for additional rigidity...
I have a visual that will allow me to get the biggest part of the table and the X rails pretty darn close and then be able to adjust the “X” linear rails and get them really fine tuned

Then for the “Z” it would also be aluminum plate with perhaps the 16 size used? or at the least one size smaller then I used for the X-Y axis...thoughts?
Reason being that the mass would not be as great as the other mentioned axis...

Then there's the depth from the top of the frame without any spoil board to the bottom of the gantry...How far...What's a general rule of thumb? 12"? 6"? and if I go 12" then what size of linear rail and ball screws should I order for the Z axis? got to keep that as ridged as possible for cutting aluminum but would like to accommodate a nice piece of wood perhaps sometime...

Then there’s another concern I had noticed on allot of the videos I watched
Gantry…would you put both linear rails on the vertical front face or one on top and one on the bottom…My thoughts here one on top and one on bottom was to reduce the amount of weight sticking out beyond the face of the Gantry which should help with rigidity…Also seems to me that the weight would be better dispersed then both hanging on the side? Thoughts?
Then there’s the location of the linear rails for the “X” and along the same thoughts would be mount them on top strictly of the weight distribution…Thoughts?

Hope I did not scare you off with these questions...
Paul